Garnets: structure, compressibility, dynamics, and disorder

The structure and properties of anhydrous end members of the garnet family were investigated by quantum mechanical calculations as a function of appli ed pressure. The results were used ro analyze the compression mechanism of the garnet structure. Hydro-grossular and hydropyrope were also studied at ambient and high pressure; the experimentally observed difference in the st ability of the hydrogarnet substitution in grossular and pyrope is explaine d here. In addition, the potential energy surface for magnesium in the pyro pe structure is discussed in relation to vibrational properties and to poss ible cation disorder in pyrope.